She claimed the Government should regulate the food and drinks industry to protect people against excess calorie intake.

Dame Sally said: “We need to be both strong and prepared to regulate. I think that the science will find sugar is addictive.

“We haven’t managed to get over to the public how calorie packed fruit juices are, smoothies are, colas and carbonated drinks are.

“We need to have a big education to know that one is fine but not lots of them. We may need to move to some sort of sugar tax – but I hope we don’t have to.”

In January, a group of health experts established the Action on Sugar campaign group, which works to reduce the amount of sugar added to food and soft drinks and educate the public about “hidden sugars”.

Flavoured water, sports drinks, yoghurts, ketchup, ready meals and even bread have been identified by the group as some everyday foods that contain large amounts of sugar.

She said: “I worry that we have re-sized a women’s dress size. We have normalised being overweight. We have to find a new way, not of ostracising people who are obese and making them feel bad about themselves, but somehow helping them to understand this is pathological and will cause them harm.

“We have a generation of children who because they are overweight and lack activity may not live as long as my generation. They will be the first generation who will live less.”

A National Obesity Forum report warned in January that predictions that half the nation will be too fat by 2050 were, in fact, an underestimate.

It said the obesity epidemic could be far worse because experts did not factor in the extent to which we put on weight as we age or the scale of the problem in children.